IR2085S

V

_{CC (max)}

25V V

offset(max)

100Vdc High/low side

output freq (f

_osc

) 500kHz Output Current (I

_O

) +/-1.0A High/low side pulse

width matching +/- 25ns

HIGH SPEED, 100V, SELF OSCILLATING 50% DUTY CYCLE, HALF-BRIDGE DRIVER

Features

•

Simple primary side control solution to enable half-bridge DC-Bus Converters for 48V distributed systems with reduced component count and board space.

•

Integrated 50% duty cycle oscillator & half-bridge driver IC in a single SO-8 package

•

Programmable switching frequency with up to 500kHz max per channel

•

+/- 1A drive current capability optimized for low charge MOSFETs

•

Adjustable dead-time 50nsec – 200nsec

•

Floating channel designed for bootstrap operation up to +100Vdc

•

High and low side pulse width matching to +/- 25nsec

•

Adjustable overcurrent protection

•

Undervoltage lockout and internal soft start

Package

Description

The IR2085S is a self oscillating half-bridge driver IC with 50% duty cycle ideally suited for 36V-75V half-bridge DC-bus converters. This product is also suitable for push-pull converters without restriction on input voltage.

Each channel frequency is equal to f_osc, where f_osc can be set by selecting R_T & C_T, where

f_osc≈ 1/(2*R_T.C_T). Dead-time can be controlled through proper selection of C_T and can range from 50 to 200nsec.

Internal soft-start increases the pulse width during power up and maintains pulse width matching for the high and low outputs throughout the start up cycle. The IR2085S initiates a soft start at power up and after every overcurrent condition. Undervoltage lockout prevents operation if V_CC is less than 7.5Vdc.

Simplified Circuit Diagram

Product Summary

S O -8 S O -8

Vb

GND LO HO

Vs

Cs OSC Vcc R

D C

S_R1

S_R2

Vo

R C L

IR2085S

Vbias (10-15V)

S

S C₂

C₁

1

2

Vin ( 100V max)

T

CT

C_BIAS

BOOT BOOT

Absolute Maximum Ratings

Absolute maximum ratings indicate sustained limits beyond which damage to the device may occur. All voltage param- eters are absolute voltages referenced to COM. All currents are defined positive into any lead. The thermal resistance and power dissipation ratings are measured under board mounted and still air conditions.

Symbol Definition Min. Max. Units

V_b High side floating supply voltage -0.3 150

V_CC Low side supply voltage — 25

V_S High side floating supply offset voltage V_b - 25 V_b + 0.3

V_HO High side floating output voltage V_b - 0.3 V_b + 0.3

V_LO Low side output voltage -0.3 V_CC + 0.3

OSC OSC pin voltage -0.3 V_CC + 0.3

V_CS Cs pin voltage -0.3 V_CC + 0.3

dV_S/dt Allowable offset voltage slew rate -50 +50 V/ns

I_CC Supply current — 20 mA

P_D Package power dissipation — 1.0 W

Rth_JA Thermal resistance, junction to ambient — 200 °C/W

T_J Junction temperature -55 150

T_S Storage temperature -55 150

T_L Lead temperature (soldering, 10 seconds) — 300

°C

Recommended Operating Conditions

For proper operation the device should be used within the recommended conditions.

Vb High side floating supply voltage V_dd -0.7 15

V_S Steady state high side floating supply offset voltage -5 100

V_CC Supply voltage 10 15

I_CC Supply current (Note 2) — 5 mA

R_T Timing resistor 10 100 KΩ

C_T Timing capacitor 47 1000 pF

fosc(max) Operating frequency (per channel) — 500 _KHz

T_J Junction temperature -40 125

°

C

Vdc

Symbol Definition Min. Max. Units

Note1: Care should be taken to avoid output switching conditions where the Vs node flies inductively below ground by more than 5V.

V

Static Electrical Characteristics

V_BIAS (V_CC, V_BS) = 12V, C_LOAD = 1000 pF and T_A = 25°C unless otherwise specified.

Symbol Definition Min. Typ. Max. Units Test Conditions

V_OH High level output voltage, (V_BIAS - V_O) — — 1.5

V_OL Low level output voltage — — 0.1

Ileak Offset supply leakage current — — 50

I_QBS Quiescent V_BS supply current — — 150

I_QCC Quiescent V_CC supply current — — 1.5 mA

V_CS+ Overcurrent shutdown threshold 250 300 350 mV

V_CS- Overcurrent shutdown threshold 150 200 250 mV

U_VCC+ Undervoltage positive going threshold 6.8 7.3 7.8 U_VCC- Undervoltage negative going threshold 6.3 6.8 7.3 U_VBS+ High side undervoltage positive going threshold 6.8 7.3 7.8 U_VBS- High side undervoltage negative going threshold 6.3 6.8 7.3

I_O+ Output high short circuit current 1.0 1.2 —

I_O- Output low short circuit current 1.0 1.2 —

Dynamic Electrical Characteristics

V_BIAS (V_CC, V_BS) = 12V, C_LOAD = 1000 pF, and T_A = 25°C unless otherwise specified.

V

µA

Symbol Definition Min. Typ. Max. Units Test Conditions

tr Turn-on rise time — 40 60

tf Turn-off fall time — 20 30

fosc Per channel output frequency 500 — — KHz

tdt High/low output dead time 50 — —

tdcs Overcurrent shut down delay — 200 — pulse on CS

PM High/low pulse width mismatch -25 — 25 V_S = 0V ~ 100V

nsec V_S = 0V

nsec

C_T =100pF, R_T =10Kohm

V

A

Lead Assignments Functional Block Diagrams

Lead Definitions

Symbol Description

VCC Logic supply GND Logic supply return Vb High side floating supply VS Floating supply return HO High side output LO Low side output CS Current sense input OSC Oscillator pin

Vb

HO

VS

LO

IR2085S

VCC OSC

CS

GND 1

2

3

8

7

6

5 4

UVLO BIAS

OSC BLOCK

PULSE STEERING

+ OVC

-

UVLO AND

RS LATCH

SOFT START

10PF

VCC

VREF (250mV)

VCC Vb

HO

VS

LO CT

GND

IR2085S BLOCK DIAGRAM

CS OSC RT

Fig. 1 Typical Output Frequency (-25^oC to 125^oC) Fig. 2 Typical Dead Time (@25^oC)

Fig. 3 Typical Dead Time vs Temperature

0 50 100 150 200 250 300 350 400 450 500

10 20 30 40 50 60 70 80 90 100

RT (kohms)

Frequency (kHz)

CT = 47pF

CT = 100pF CT = 220pF

CT = 470pF

50 75 100 125 150 175 200 225 250

10 20 30 40 50 60 70 80 90 100

RT (kohms)

Time (ns) CT = 470pF

CT = 220pF CT = 100pF

CT = 47pF

60 80 100 120 140 160 180

-40 -20 0 20 40 60 80 100 120

Temperature

Dead Time (ns)

DT(CT=100pF, RT=100k)

Pin descriptions

CS: The input pin to the overcurrent comparator. Ex- ceeding the overcurrent threshold value specified in static electrical parameters section will terminate the output pulses and start a new soft-start cycle as soon as the voltage on the pin reduces below the threshold value.

OSC: The oscillator-programming pin. Only two com- ponents are required to program the oscillator fre- quency, a resistor (tied to the V_CC and CS pins), and a capacitor (tied to the CS and GND pins). The approxi- mate oscillator frequency is determined by the follow- ing simple formula:

f_OSC = 1/ (2*R_T.C_T)

Where f_OSC frequency is in hertz (Hz), R_T resistance in ohms (Ω) and C_T capacitance in farads (F). The recommended range for the timing resistor is between 10kW and 100kW and the recommended range for the timing capacitor is between 47pF and 470pF. It is not recommended to use timing resistors less than 10kΩ.

For best performance, keep the timing component placement as close as possible to the IR2085S. It is recommended to separate the ground and V_CC traces to the timing components.

GND: Signal ground and power ground for all func- tions. Due to high current and high frequency opera- tion, a low impedance circuit board ground plane is highly recommended.

HO, LO: High side and low side gate drive pins. The high and low side drivers can be used to drive the gate of a power MOSFET directly, without external buffers. The drivers are capable of 1.2A peak source and sink currents. It is recommended that the high and low side drive pins should be located very close to the gates of the high side and low side MOSFETs to prevent any delay and distortion of the drive sig- nals. The power MOSFETs should be low charge to prevent any shoot through current.

V_b: The high side power input connection. The high side supply is derived from a bootstrap circuit using a low-leakage schottky diode and a ceramic capacitor.

To prevent noise, the schottky diode and bypass ca- pacitor should be located very close to the IR2085S and separated V_CC traces are recommended.

V_S: The high side power return connection. V_S should be connected directly to the source terminal of the high side MOSFET with the trace as short as pos- sible.

V_CC: The IC bias input connection for the device. Al- though the quiescent V_CC current is very low, total sup- ply current will be higher, depending on the MOSFET gate charge connected to the HO and LO pins, and the programmed oscillator frequency. Total V_CC cur- rent is the sum of quiescent V_CC current and the aver- age current at HO and LO. Knowing the operating frequency and the MOSFET gate charge (Q_G), the average current can be calculated from:

I_ave = Q_G X f_osc

To prevent noise problems, a bypass ceramic capacitor connected to V_CC and GND should be placed as close as possible to the IR2085S.

The IR2085S has an under voltage lockout feature for the IC bias supply, V_CC. The minimum voltage required on V_CC to make sure that the IC will work within speci- fications is 9.5V. Asymmetrical gate signals on HO and LO pins are expected when V_CC is between 7.5V and 8.5V.

Application Information

A 220 kHz half-bridge application circuit with full wave synchronous rectification is shown in figure 4. On the primary side, the IR2085S drives two IRF7493 - next generation low charge power MOSFETs. The primary side bias is obtained through a linear regulator from the input voltage for start-up, and then from the trans- former in steady state. The IRF7380, a dual 80V power MOSFET in an SO8 package is used for the primary side bias function. Two IRF6603 - novel DirectFET

power MOSFETs are used on the secondary side in a self-driven synchronous rectification topology.

DirectFETs practically eliminate MOSFET packaging resistance, which maximizes circuit efficiency. The DirectFET construction includes a copper “clip” across the backside of the silicon, which enables top-sided cooling and improved thermal performance. The DirectFET gate drive voltage is clamped to an opti- mum value of 7.5V with the IRF9956 dual SO-8 MOSFET. The secondary side bias scheme is de- signed to allow outputs of two bus converters to be connected in parallel, while operating from different input voltages, and also to allow continuing output current if one of the two input sources is shorted or disconnected.

Two ferrite cores are used for the transformer and inductor. The transformer core is a PQ20/16 (3F3) with 3:1 turns ratio and 1mil gap. The inductor core is an E14/3.5/5 (3F3) with one turn and a 5mil gap. The PCB has eight layers, with two layers for primary windings that are connected in parallel and each has three turns. Four layers are used for the secondary windings. Each layer has one turn and two layers are connected in parallel to get two sets of secondary windings. 4 oz Cu PCB is recommended for the primary and secondary windings. Each primary side winding is placed between the two sets of the secondary windings to balance the secondary side current.

Figure 4 – IR2085S DC Bus converter reference design.

36~60Vinput 3.3u 39k

Vdd

22u

IRF6603 IRF6603 IRF7493

IRF7493

22u 200

3.3u

IRF9956 1

3

1

3 7

7

3 9 9

1u Vdd

cs ct G LO Vcc

Vb Vs HO IR2085 56k

9V .1u

1u

1u 47

100k

10k

10k Vdd

36~60Vinput

.1u 39k

200 IRF7380

15V 3V

rm

6~10Vout

S

47p 56k

01-6027 01-0021 11 (MS-012AA)

8-Lead SOIC

8 7 5

6 5

D B

E A

e 6X

H 0.25 [.010] A 6

4 3 1 2

4. OUTLINE CONFORMS TO JEDEC OUTLINE MS-012AA.

NOTES:

1. DIMENSIONING & TOLERANCING PER ASME Y14.5M-1994.

2. CONTROLLING DIMENSION: MILLIMETER 3. DIMENSIONS ARE SHOWN IN MILLIMETERS [INCHES].

7 K x 45°

8X L 8X c

y

FOOTPRINT 8X 0.72 [.028]

6.46 [.255]

3X 1.27 [.050] 8X 1.78 [.070]

5 DIMENSION DOES NOT INCLUDE MOLD PROTRUSIONS.

6 DIMENSION DOES NOT INCLUDE MOLD PROTRUSIONS.

MOLD PROTRUSIONS NOT TO EXCEED 0.25 [.010].

7 DIMENSION IS THE LENGTH OF LEAD FOR SOLDERING TO A SUBSTRATE.

MOLD PROTRUSIONS NOT TO EXCEED 0.15 [.006].

0.25 [.010] C A B

e1 A

8X b A1

C

0.10 [.004]

e 1 D E

y b A A1

H K L

.189 .1497

0°

.013

.050 BASIC .0532 .0040

.2284 .0099 .016

.1968 .1574

8°

.020 .0688 .0098

.2440 .0196 .050

4.80 3.80 0.33 1.35 0.10

5.80 0.25 0.40 0°

1.27 BASIC 5.00 4.00 0.51 1.75 0.25

6.20 0.50 1.27

MIN MAX

MILLIMETERS INCHES

MIN MAX

DIM

8°

e

c .0075 .0098 0.19 0.25

.025 BASIC 0.635 BASIC

Case outline

WORLD HEADQUARTERS: 233 Kansas Street, El Segundo, California 90245 Tel: (310) 252-7105 http://www.irf.com/ Data and specifications subject to change without notice. 3/25/2003